A glycoprotein exhibiting immunological and enzymatic activities of human prostatic acid phosphatase has been purified and amino-terminal sequences of both prostatic acid phosphatase and glycoprotein were found to be different. A human prostate antigen was purified from both prostate gland and seminal plasma and its physico-chemical properties characterized. Four ribonucleases have been purified to homogeneity and characterized from human seminal plasma. The seminal RNase III was found to be a prostate-specific enzyme, whereas others are similar to serum RNases. Amino acid sequence of human dihydrofolate reductase has been determined, and the primary structure information is also helpful to understand the structure-function relationship of dihydrofolate reductase. The primary structure information of protein is very important in elucidating the fundamental biological function. The collaborative research of protein sequencing will provide expertise so that fast and accurate information can be obtained for cloning and identification of eukaryotic genes.